void var_dump ( mixed expression [, mixed expression [, ...]] )

var_dump()方法是判断一个变量的类型与长度,并输出变量的数值,如果变量有值输的是变量的值并回返数据类型.

此函数显示关于一个或多个表达式的结构信息，包括表达式的类型与值。数组将递归展开值，通过缩进显示其结构。

例1：

1. $a = "alsdflasdf;a";
2. $b = var_dump($a);
3. echo "
4. ";
5. //var_dump($c);
6. $d=var_dump($c);
7. echo "
8. ";
9. echo $a;
10. echo "
11. ";
12. echo $b;
13. echo "
14. ";
15. 输出：
16. string(12) "alsdflasdf;a"
17. NULL
18. alsdflasdf;a

例2：1. var_dump() 示例

1. $a = array (1, 2, array ("a", "b", "c"));
2. var_dump ($a);
3. /* 输出： array(3) { [0]=> int(1) [1]=> int(2) [2]=> array(3) { [0]=> string(1) "a" [1]=> string(1) "b" [2]=> string(1) "c" } }
4. */
5. $b = 3.1; $c = TRUE; var_dump($b,$c);
6. /* 输出： float(3.1) bool(true)
7. */ ?>

var_export和serialize做数组缓存

$str = serialize($arr); 这两种机制转换之后的字符串是不一样的，第一种是数组的原型模式，第二种是序列化后的形式。第一 种存入文件中的只要加上标签，就形式了一个可用的数组原型，对调用来说，不用转换，直接返回这个数组就可以，但第二种，则需要再用一次unserialize函数反序 列化一下。对于第种一说，就多了一步操作。下来我们用数据说话吧:

1. set_time_limit(50); $a = array(1,2,3); $b = array('a'=>1, 'b'=>2, 'c'=>3); $c = array('a'=>array(1,2,3), 'b'=>array(4,5,6));
2. $time1 = microtime(true);
3. $times = 1000000; #10w
4. for($i=1; $i<=$times; $i++){ $A = var_export($a, true); }
5. $time2 = microtime(true);
6. for($i=1; $i<=$times; $i++){ $B = var_export($b, true); }
7. $time3 = microtime(true);
8. for($i=1; $i<=$times; $i++){ $C = var_export($c, true); }
9. $time4 = microtime(true);
10. for($i=1; $i<=$times; $i++){ $X = serialize($a); }
11. $time5 = microtime(true);
12. for($i=1; $i<=$times; $i++){ $Y = serialize($b); }
13. $time6 = microtime(true);
14. for($i=1; $i<=$times; $i++){ $Z = serialize($c); }
15. $time7 = microtime(true);
16. for($i=1; $i<=$times; $i++){ $O = unserialize($X); }
17. $time8 = microtime(true);
18. for($i=1; $i<=$times; $i++){ $P = unserialize($Y); }
19. $time9 = microtime(true);
20. for($i=1; $i<=$times; $i++){ $Q = unserialize($Z); } $time10 = microtime(true);
21. $var_export_time['a'] = $time2 - $time1; $var_export_time['b'] = $time3 - $time2; $var_export_time['c'] = $time4 - $time3;
22. $serialize_time['a'] = $time5 - $time4; $serialize_time['b'] = $time6 - $time5; $serialize_time['c'] = $time7 - $time6;
23. $unserialize_time['a'] = $time8 - $time7; $unserialize_time['b'] = $time9 - $time8; $unserialize_time['c'] = $time10 - $time9; print_r($var_export_time); print_r($serialize_time); print_r($unserialize_time); ?> output: Array( [a] => 3.3401498794556 [b] => 5.1394801139832 [c] => 8.8483898639679)Array( [a] => 1.6063709259033 [b] => 1.7033960819244 [c] => 3.4534389972687)Array( [a] => 1.6037359237671 [b] => 1.817803144455 [c] => 3.7992968559265)

由上面数据说明： var_export函数性能比serialize函数性能差一倍，而 unserialize时间也需要和serialize差不多的时间，serialize加上unserialize时间，和用var_export时间 差不多。